The present invention relates to an adjustable speed drive system for a primary loop recirculation pump for a nuclear reactor coolant, which is suitable for driving and controlling a primary loop recirculation pump which controls power output of a nuclear reactor of a nuclear power plant.
Conventionally, a flow control of a reactor core has been performed by a primary loop recirculation pump (a PLR pump) in order to control a nuclear reactor power output. In a BWR (stands for Boiling-Water Reactor) plant, the power output control of the nuclear reactor has been performed by employing PLR pumps in the two system configuration, and an MG set has been used as its power supply system for variably controlling a rotating speed of a motor which is connected to the primary loop recirculation pump. The MG set is constituted to include an induction motor, which is connected to each of two system of high voltage buses in the plant via an incoming breakers, and rotated by an electric power supplied from the high voltage bus, a variable-speed fluid coupling connected to a rotating shaft of the induction motor, and a generator connected to the variable-speed fluid coupling. The generator has a motor connected thereto via a breaker for tripping a primary loop recirculation pump (hereinafter referred to as RPT breaker), so that an electric power generated by the generator is supplied to the motor via the RPT breaker, and the rotating speed of the generator is controlled by the variable fluid coupling to control electric voltage and frequency supplied to the motor to thereby control the rotating speed of the primary loop recirculation pump so as to eventually control the flow amount of the nuclear reactor coolant.
In the conventional technique using the MG set, when a turbine trip or a load rejection occurs during the plant operation, the MG set is used together with the scram of the nuclear reactor to make shutting down of the RPT beaker and to trip the two PLR pumps so as to rapidly reduce the flow of the reactor core to thereby moderating a transient increase in power output from the nuclear reactor, so that sound performance of the fuel is maintained.
In recent years, by virtue of a development of a power semiconductor device with large capacity, a static variable-frequency power supply (an inverter) using the power semiconductor device, instead of the MG set, came into use. As a result, the conventional MG set has been becoming obsolete, and gradually the static variable-frequency power supply has been instead adopted. JP-A-8-80061 discloses an power supply system for a primary loop recirculation pump adopting a current source inverter.
Compared to the primary loop recirculation pump using the MG set, a power generation plant adopting the inverter power supply system does not require the MG set which consists of an induction motor, a variable-speed fluid coupling, a generator, and an oil system as an auxiliary machinery, therefore, there are some advantages such as enhancement of maintainability, effectiveness during low power output, and linearity of speed control, and the like.